Coils for inductive apparatus



Feb. 22, 1966 J. G. FORD COILS FOR INDUCTIVE APPARATUS 4 Sheets-Sheet 1 Original Filed Sept. 29, 1961 INVENTOR John 6. Ford YEM ATTORNEY Feb. 22, 1966 Original Filed Sept.

J. G. FORD COILS FOR INDUCTIVE APPARATUS 4 Sheets-Sheet 2 4 Sheets-Sheet 5 J. G. FORD COILS FOR INDUGTIVE APPARATUS TAG -QA4M/A/Z VQV/MV MVAT Av @747 Feb. 22, 1966 Original Filed Sept. 29, 1961 A .m F

4 Sheets-Sheet 4 I75 TEMPERATURE C J. G. FORD COILS FOR INDUCTIVE APPARATUS Feb. 22, 1966 Original Filed Sept. 29, 1961 United States Patent 3,237,136 COILS FOR INDUCTIVE APPARATUS James G. Ford, Hickory Township, Sharpsville, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Continuation of application Ser. No. 141,738, Sept. 29,

1961. This application Nov. 19, 1964, Ser. No. 414,503

Claims. (Cl. 336-205) This application is a continuation of copending application Serial No. 141,738, now abandoned, filed September 29, 1961, in the name of James G. Ford, and assigned to the same assignee as the present application.

This invention relates in general to electrical inductive apparatus and more particularly to coils for electrical apparatus, such as transformers.

Coils of the prior art have conventionally used a coil form wound from an insulating paper having a discontinuous coating of epoxy or other suitable resin on both sides. The process of depositing the resin on the paper is an expensive one. Also, with the paper coated on both sides and layers of the paper wound one on top of another, it becomes very difiicult to completely impregnate the coil form with a liquid dielectric so that small pockets of air are not trapped within the paper under the resin. When the coil is subjected to high voltages, the trapped air ionizes causing corona which, of course, interferes with radio, television and other electrical equipment which is responsive to low value electrical signals.

Accordingly, it is the general object of this invention to provide an improved coil for electrical inductive apparatus such as transformers.

It is a more particular object of this invention to provide an inexpensive coil for a transformer that has a very low value of radio interfering signal radiation.

Briefly, the present invention accomplishes the abovecited objects by providing a coil form wound from an insulating paper having a discontinuous coating of resin on only one side. The wire used to wind the coil is an insulated-wire with a layer of an adhesive thereon that is either thermosetting or of sutficiently high melting point so as not to flow appreciably at operating temperatures. The adhesive is tack free at ambient temperature but at elevated temperature it becomes semifluid. Then when cooled it permanently sets so that the turns of the coil are bonded to each other as well as to the coil form to give a much less expensive and a more rigid coherent coil and coil form. The total build-up of material on the double coated wire is no greater than the build-up of the enamel coating on the prior art enameled wire. Also, with the resin on only one side of the paper the liquid dielectric can easily impregnate the entire coil form thereby eliminating the air pockets and the resulting radio interference. However, by proper selection of pattern of resin coating it is possible to coat both sides of the paper to allow for thorough impregnation with liquid dielectric.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of the specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a side view of a transformer coil made according to my invention;

FIG. 2 is a sectional view of the coil of FIG. 1 taken along the line IIII of FIG. 1;

FIG. 3 is a sectional view of a coil having only one section of low voltage winding and one section of high voltage winding;

FIG. 4 is a View of the insulating paper showing the pattern of the adhesive deposited thereon;

FIG. 5 is an enlarged view of the double coated wire showing the enamel coating with a coating of adhesive thereon;

FIG. 6 is a curve of the turn-to-turn dielectric strength of the double coated wire as a function of temperature; and

FIG. 7 is a curve of the layer-to-layer dielectric strength of the wire of FIG. 4.

The coil illustrated by FIGS. 1 and 2 is formed by winding two turns of a sheet of thermally stabilized insulating paper 10 having on one side thereof a discontinuous coating of an adhesive, such as epoxy resin, phenolic, epoxy-phenolic or other suitable resin, which is in the B stage. That is, the adhesive is tack free at ambient temperature, becomes soft and flows at elevated temperatures, then permanently sets when cooled. This set can be accomplished by polymerization or condensation, or both, resulting in increased molecular weight and melting point. The two turns of paper 10 form the coil form. Although, the coil form as described throughout is made from multiple layers of paper wound on a mandrel, a solid coil form could be used. The inside layer 12 of the inside section of the low voltage winding of a transformer is wound directly on the coil form 10. The low voltage winding is shown in FIG. 2 as a plurality of turns of rectangular wire 14 wound in two layers 12 and 16 with two turns of thermally stabilized insulating paper 18 between the layers 12 and 16. The wire 14 has a coating of insulation thereon with a layer of adhesive over the coating of insulation. The adhesive on the wire 14, for example, an epoxy resin, epoxy vinyl formal, high molecular weight vinyl formal or modified phenolics, in the B stage, and is t ack free at ambient temperature but at elevated temperatures becomes soft and flows around the individual wires 14. When cooled the adhesive permanently sets to thereby bond the coil form 10, the two layers of the winding 12 and 16 and the layer-to-layer insulation 18 rigidly together. The insulation 18 has the discontinuous coating of adhesive on one side only. Although, as used in my invention, the paper has the adhesive on one side only it could be coated on both sides, if so desired.

The next layer 20 is paper insulation wound around the outside layer 16 of the inside section of the low voltage winding. The thermally stabilized insulating paper 20 has adhesive on one side.

A plurality of pressboard or wood strips 22 provide a duct 24 for the circulation of a liquid dielectric adjacent to the end turns of the outside section 16 of the low voltage winding. The pressboard or other insulating strips 22 are glued to the last turn of the insulating tube 20 around the ends of the transformer to provide a space or duct between the tube 20 formed by the two turns of insulating paper and the insulating tube 26. This space or duct allows the liquid dielectric to circulate between the low voltage winding and the high voltage winding to thereby cool the windings.

The tube 26 is formed by winding on top of the tube 20 as many layers of insulating paper as required to insulate the low voltage winding from the high voltage winding. The paper used to form the tube 26 is also a thermally stabilized paper with the discontinuous coating of resin on one side thereof. The inside section 29 of the high voltage winding is comprised of a plurality of layers of wire 28 wound on the tube 26 with a turn of stabilized insulating paper between each layer of wire. The wire 28, like the wire 14, is insulated wire, such as enameled wire, with a coating of adhesive thereon. This wire 28 is shown in more detail in FIG. 5. The paper between the layers of the high voltage winding is crimped or cuffed at the ends to prevent any movement of the layers of Wire in an axial direction to thereby make a more rigid coil. The cuffed paper wound between the layers of wire does not need a coating of adhesive on either side because the adhesive on the wire bonds the layer of insulation and the layer of wire solidly together.

A strip of corrugated fibrous sheet 30 is placed on the first section of high voltage winding 29 at the ends of the transformer. The corrugated strip 30 provides a duct 32 for circulation of the liquid dielectric between high voltage sections 29 and 36. The corrugated strip 30 has a coating of adhesive on one side thereof.

Two turns of thermally stabilized insulating paper 34, having an adhesive on one side, are wound on the corrugated fibrous strip 30. A second section of high voltage winding 36 is then wound on the insulating tube 34 in the same manner as the first section 18. That is, alternatelayers of wire and insulating paper which is cuffed at the ends. FIG. 2 shows three high voltage sections 29, 36 and 38 with a corrugated fibrous strip 30 between each section. However, as many sections would be used as required for proper cooling of the winding at the particular transformer rating.

On the last section 38 of high voltage winding another duct 24 is provided for the circulation of the liquid dielectric adjacent to the last section 38 of high voltage winding. FIG. 1 shows the duct 24 formed at the ends of the transformer by pressboard strips 22.

A tube 40 wound on the duct 24 from the thermally stabilized insulating paper having the adhesive resin on one side provides the necessary insulation between the outside section 38 of the high voltage winding and the inside layer 42 of the outside section of the low voltage winding.

The outside section of the low voltage winding, like the inside section, is comprised of two layers 42 and 44 of enamel insulated wire 14 with a coating of adhesive resin on the enamel insulation and a layer of stabilized insulating paper 46 between each layer of the winding. The double coated wire has the same amount of build-up of insulation plus adhesive as the prior art standard enameled wire. Therefore, there is no increase in thespace required and substantially no increase in the cost because the same number of passes through the coating tower are required to insulate the wire.

The entire transformer has a turn of the stabilized insulating paper 48 wound on the outside layer 44 of the outside section of the low voltage winding.

After the entire transformer coil is wound, it is placed in an oven and heated under pressure to 150 C. to 175 C. This causes the adhesive on the insulating paper and wires to become soft and flow. The transformer coil is then cooled and the adhesive permanently hardens and bonds the various layers of the transformer coil together to form a solid coherent unit. The adhesive also has good insulating characteristics and tends to heal the cracks and weakened spots in the wire insulation caused by winding to thereby restore the dielectric strength to a value approximately equal to the value obtained before bending or working. It has been found from experience that when insulated wire comes from the enameling tower, it has a certain dielectric strength, but after the wire has been reeled on and off a spool and worked by winding into the coil, the insulation loses about half its dielectric strength because of nicks and cracks or other damage caused in the reeling and unreeling and winding operations. However, it has also been found that when the adhesive coated wire is heated to a temperature high enough to cause the adhesive to soften and flow the adhesive cures most of the damage done to the dielectric characteristics in working the wire and that the final coil assembly has dielectric characteristics close to the enamel insulated wire as it comes out of the enameling tower and before the wire'has been worked. The adhesive after v to wind the coil.

it flows, materially improves the transformer coil since it substantially increases the dielectric strength of the wire insulation. It also firmly bonds the winding turns to each other and to the paper insulation to provide a solid, sturdy, structure and because of these advantages permits the building of a less expensive transformer because the number of reject coils is substantially reduced. This structure provides good mechanical stability under short circuit conditions thus reducing potentiality of failure in service.

The sectional view of FIG. 3 shows a transformer with only one section of low voltage winding and one section of high voltage winding 128. Like the multi-section transformer of FIGS. 1 and 2, the transformer of FIG. 3 has a strip of thermally stabilized paper wound on a mandrel to form a tube 110. A two layer 112 and 116 low voltage winding 90 with an insulating layer 118 between the layers is wound on the tube 110. A layer of insulation 120 and a duct 124, for the circulation of the liquid dielectric, are wound on the low voltage winding 90. A strip of insulating paper having a discontinuous coating of adhesive on one side, is then wound on the duct 124 to form a tube 126 of sufficient thickness to insulate the low voltage winding 90 from the high voltage winding 128. The high voltage winding 128 is then wound on the insulating tube 126 with a layer of paper, cuffed at the ends, wound between each layer of the high voltage winding. The cuffed paper does not have the resin on either side. The final layer 131 is insulation wound from the thermally stabilized paper with a discontinuous adhesive coating on one side.

FIG. 4 shows the pattern of the adhesive applied to the insulating paper used throughout the transformer. The paper is a thermally stabilized paper having a discontinuous coating of an epoxy or other suitable resin 102 on one side thereof. The resin is in its B stage, that is, it is tack free at ambient temperature and when heated becomes soft. The resin when cooled permanently sets thereby securely bonding the several turns of material described in connection with FIGS. 1 and 2 into a rigid coherent unit. When the resin is applied to the paper in the spotted pattern shown, that is, small areas on one side of the paper only, the paper is easily impregnated with the liquid dielectric thereby eliminating any air pockets and preventing radio interference.

FIG. 5 is an enlarged perspective view of the wire used An insulated Wire, such as enameled wire is used. However, the thickness of the enamel 202 on the conductor 200 is thinner than normal. A coating of an epoxy or othersuitable bonding resin 204 is then placed on the enameled wire to give the standard build-up of insulation on the wire. That is an increase of from 0.0015 inch to 0.005 inch on the diameter of the wire. The resin can be the same as that used on the insulating paper. When heated the resin coating 204 on the wire flows to thereby heal the cracks or nicks and other weakened spots in the insulation, caused by the winding operation, which, of course, increases the turn-to-turn and layer-to-layer dielectric strength of the coil. The resin also flows around the wire to fill the areas between the turns. When cooled the resin permanently sets to bond the wires together and to the layer-to-layer insulating paper thereby giving a very rigid coil. Conductors having an enamel insulation coating with a layer of resin on top of the enamel coating are used for both the high voltage and the low voltage windings of the coil.

The following table is a tabulation of the layer to layer and turn to turn dielectric strength of double coated number 20 magnet Wire as a function of temperature of cure and the ratio of adhesive to insulation. It will be noticed from the tabulation and the curves of FIGS. 6 and 7 that the dielectric strength increases as the thickness of the adhesive decreases; although, the overall build-up of enamel plus adhesive remains constant. Also, notice the increase in dielectric strength when the double coated wire is heated in the curing operation.

Test data for a 0.032 inch diameter wire with a 0.0019 inch build-up of adhesive plus enamel showed an, as produced, average dielectric strength of 2263 volts per mil which increased to an average dielectric strength of 3442 volts per mil after heating one hour at 150 C. Upon removalof the wire from the drum for this test several snags were encountered and the increase in dielectric strength when heated is attributed to the healing effect of the adhesive coating on the damage caused to the enamel by the snags.

said first winding having an insulating material disposed thereon and a continuous adhesive coating over said insulating material; a second tubular insulating member having a plurality of superposed layers of insulating material and disposed on said first winding; a single resinous coating of adhesive disposed between the superposed layers of insulating material of said second tubular insulating member in a predetermined spotted pattern; a second winding having a plurality of conductor turns disposed on said second tubular insulating member; the plurality of conductor turns of said second winding having an insulating material thereon with a continuous adhesive Wire Treatment, Inches Buildup Average Dielectric Strength in Volts/Mil AIEE Standard Vinyl Formal Urea Formalde- Twist Test at No 1 Hour Bake With 50 P.S.I. Load and Epoxy hyde Vinyl Load Resin Formal Epoxy Adhesive Enamel Insllation 1 Hour Turn to Turn Layer to Layer As Bake, Produced 100 0.,

No Load 125 0. 150 C. 175 C. 125 C. 150 0. 175 C FIGS. 6 and 7 are curves of the turn-to-turn and layerto-layer dielectric strength, respectively, of the insulation on the wire as a function of temperature. The dotted curves 302 and 304 are the turn-to-turn and layer-to-layer dielectric strength, respectively, with 0.0006 inch of vinyl formal plus epoxy resin adhesive and 0.0028 inch of urea formaldehyde vinyl formal epoxy enamel. The dashed curves 306 and 308 are the turn-to-turn and layer-to-layer dielectric strength, respectively, of the insulation of 0.001 inch of adhesive and 0.0025 inch of enamel. The dotdash curves 310 and 312 are the turn-to-turn and layerto-layer dielectric strength, respectively, of the insulation with 0.0011 inch of adhesive and 0.0022 inch of enamel on the wire. The solid curves 314 and 316 show the turnto-turn and layer-to-layer dielectric strength, respectively, versus temperature of cure for insulation having 0.0019 inch of adhesive and 0.0016 inch of enamel.

The described method of winding transformer coils greatly decreases the costs of the transformers, since it eliminates the necessity of applying the adhesive coating to one side of the insulating material which forms the tubes and eliminates coating both sides of the layer-tolayer insulation. It also greatly reduces the number of rejected coils due to the healing effect the adhesive resin has on the enamel insulation. Shop failures decreased from approximately /z% failures of coils of the prior art to substantially 0% failure when wound in accordance with my invention. Thatis, of 400, 10 kva., 7200 volt pole type distribution transformers wound in accordance with my invention there have been no shop failures. This, of course, indicates a substantial decrease in service failure.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

1 claim as my invention:

1. A coil for a transformer comprising a first tubular insulating member having a plurality of superposed layers of insulating material; a single resinous coating of adhesive disposed between the superposed layers of insulating material of said first tubular insulating member in a predetermined spotted pattern; a first winding having a plurality of conductor turns disposed on said first tubular insulating member; the plurality of conductor turns of coating over said insulating material; said adhesive coatings 0n the conductor turns of said first and said second windings firmly bonding the turns of said first winding together and to said first and second tubular insulating members, bonding the turns of said second winding together and to said second tubular insulating member, and improving the dielectric characteristics of said windings; said adhesive coating on the conductor turns of said first and second windings providing the entire bonding action between said first and second windings and said first and second tubular insulating members.

2. A coil for a transformer comprising a first tubular insulating member having a plurality of superposed layers of insulating material; a single resinous coating of ad hesive disposed between the superposed layers of insulating material of said first tubular insulating member in a predetermined spotted pattern; a first wind-ing having a plurality of conductor t-urns disposed on said first tubular insulating member; the conductor turns of said first winding having an insulating coating thereon and a continuous adhesive coating over said insulating coating; said insulating coating plus said adhesive coating on the conductor turns of said first winding having a total build-up of not over 0.0035 inch; a second tubular insulating member having a plurality of superposed layers of insulating material and disposed on said first winding; a single resinous coating of adhesive disposed between the superposed layers of insulating material of said second tubular insulating material in a predetermined spotted pattern; a second winding having a plurality of conductor turn-s disposed on said second tubular insulating member; the conductor turns of said second winding having an insulating coating with a continuous adhesive coating over said insulating coating; said insulating coating plus said adhesive coating on the conductor turns of said second winding providing a total build-up of not over 0.0035 inch; said adhesive coating on the conductor turns of said first and said second windings firmly bonding the turns of said first winding together and to said first and second tubular insulating members, bonding the turns of said second winding together and to said second tubular insulating member, and improving the dielectric characteristics of said windings; said adhesive coating on the conductor turns of said first and second windings providing the entire bonding action between said first and second windings and said first and second tubular insulating members.

3. A coil for a transformer comprising a first tubular insulating member having a plurality of superposed layers of insulating material; a single resinous coating of adhesive disposed between the superposed layers of insulating material of-said first tubular insulating member in a predetermined spotted pattern; a first winding having a plurality of conductor turns and disposed on said first tubular insulating member; the conductor turns of said first winding having an insulating coating thereon causing a total build-up of not more than 0.0028 inch and a continuous adhesive coating causing an additional total build-up of not more than 0.0019 inch on said insulating coating; a second tubular insulating member having a plurality of superposed layers of insulating material and disposed on said first winding; a single resinous coating of adhesive disposed between the superposed layers of insulating material of said second tubular insulating member in a predetermined spotted pattern; a second winding having a :plurailty of conductor turns disposed on said second tubular insulating member; the conductor turns of said second winding having an insulating coating thereon causing a total build-up of not more than 0.0028 inch and a continuous adhesive coating over said insulating coating causing an additional total build-up of not more than 0.0019 inch; said adhesive coating on the conductor turns of said first and said second windings firmly bonding the turns of said first winding together and to said first and second tubular insulating members, bonding the turns of said second winding together and to said second tubular insulating member, and improving the dielectric characteristics of said coil; said adhesive coat-ing on the conductor turns of said first and second windings providing the entire bonding action between said first and second windings and said first and second tubular insulating members.

4. A coil for a transformer comprising a first tubular insulating member formed from a plurality of superposed layers of insulating material; a discontinuous single layer coating of adhesive disposed in a predetermined regular pattern between the superposed layers of the insulating material of said first tubular insulating member; said discontinuous single layer coating of adhesive forming a plurality of uniform bonds between the adjacent layers of insulating material; a first winding having a plurality of conductor turns disposed on said first tubular insulating member; the conductor turns of said first winding having an insulating coating thereon and a continuous adhesive coating over said insulating coating; a second tubular insulating member disposed on said first winding; said second tubular insulating member being formed from a plurality of superposed layers of insulating material; a discontinuous single layer coating of adhesive disposed in a predetermined regular pattern between the super-posed layers of the insulating material of said'second tubular insulating member; said discontinuous single layer coating of adhesive forming a plurality of uniform bonds between the adjacent layers of insulating material; a second winding having a plurality of conductor turns disposed on said second tubular insulating member; the conductor turns of said second winding having an insulating coating thereon with a continuous adhesive coating over said insulating coating; said adhesive coating on the conductor turns of said first and said second windings firmly bonding the turns of said first winding together and to said first andsecond tubular insulating members, and

bonding the turns of said second winding together and to said second tubular insulating member; said adhesive coating on the conductor turns of said first and second windings providing the entire bonding action between said first and second windings and said first and second tubular insulating members.

5. A coil for a transformer com-prising a first tubular insulating member formed from a plurality of superposed layers of insulating material; a discontinuous single layer coating of adhesive disposed in a predetermined regular pattern between the superposed layers of the insulating material of said first tubular insulating member; said discontinuous single layer coating of adhesive forming a plurality of uniform bonds between the adjacent layers of insulating material and insuring that the only interfacesformed between the super-posed layers are adhesive to insulating material interfaces; a first winding having a plurality of conductor turns arranged in a plurality of layers with an insulating member between each layer; said first winding being disposed on said first tubular insulating member; the plurality of conductor turns of said first winding having an insulating coating thereon and a continuous coating of adhesive over said insulating coating; a second tubular insulating member disposed on said first winding; said second tubular insulating member being formed from a plurality of superposed layers of insulating material; a discontinuous single layer coating of adhesive disposed in a predetermined regular pattern between the superposed layers of the insulating material of said second tubular insulating member; said discontinuous coating of adhesive forming a plurality of uniform bonds between the adjacent layers of said insulating material and insuring that the only interfaces formed between the superposed layers are adhesive to insulating material interfaces; a second winding having a plurality of conductor turns arranged in a plurality of layers with an insulating member between each layer; said second winding being disposed on said second tubular insulating member; the plurality of conductor turns of said second winding having an insulating coating thereon with a continuous coating of adhesive over said insulating coating; said adhesive coating on the turns of said first winding firmly bonding said turns together, to said insulating members disposed between each winding layer, and to said first and second tubular insulating members; said adhesive coating on the turns of said second winding firmly bonding said turns together, to said insulating members disposed between each winding layer, and to said second tubular insulating member; said adhesive coating on the conductor turns of said first and second windings providing the entire bonding action between said first and second windings and said first and second tubular insulating members, and between the plurality of conductor turns of each of said first and second windings and said insulating members disposed between each winding layer.

References Cited by the Examiner UNITED STATES PATENTS JOHN F. BURNS, Primary Exiaminen, 

1. A COIL FOR A TRANSFORMER COMPRISING A FIRST TUBULAR INSULATING MEMBER HAVING A PLURALITY OF SUPERPOSED LAYERS OF INSULATING MATERIAL; A SINGLE RESINUOUS COATING OF ADHESIVE DISPOSED BETWEEN THE SUPERPOSED LAYERS OF INSULATING MATERIAL OF SAID FIRST TUBULAR INSULATING MEMBER IN A PREDETERMINED SPOTTED PATTERN; A FIRST WINDING HAVING A PLURALITY OF CONDUCTOR TURNS DISPOSED ON SAID FIRST TUBULAR INSULATING MEMBER; THE PLURALITY OF CONDUCTOR TURNS OF SAID FIRST WINDING HAVING AN INSULATING MATERIAL DISPOSED THEREON AND A CONTINUOUS ADHESIVE COATING OVER SAID INSULATING MATERIAL; A SECOND TUBULAR INSULATING MEMBER HAVING A PLURALITY OF SUPERPOSED LAYERS OF INSULATING MATERIAL AND DISPOSED ON SAID FIRST WINDING; A SINGLE RESINUOUS COATING OF ADHESIVE DISPOSED BETWEEN THE SUPERPOSED LAYERS OF INSULATING MATERIAL OF SAID SECOND TUBULAR INSULATING MEMBER IN A PREDETERMINED SPOTTED PATTERN; A SECOND WINDING HAVING A PLURALITY OF CONDUCTOR TURNS DISPOSED ON SAID SECOND TUBULAR INSULATING MEMBER; THE PLURALITY OF CONDUCTOR TURNS OF SAID SECOND WINDING HAVING AN INSULATING MATERIAL THEREON WITH A CONTINUOUS ADHESIVE COATING OVER SAID INSULATING MATERIAL; SAID ADHESIVE COATINGS ON THE CONDUCTOR TURNS OF SAID FIRST AND SAID SECOND WINDINGS FIRMLY BONDING THE TURNS OF SAID FIRST WINDING TOGETHER AND TO SAID FIRST AND SECOND TUBULAR INSULATING MEMBERS, BONDING THE TURNS OF SAID SECOND WINDING TOGETHER AND TO SAID SECOND TUBULAR INSULATING MEMBER, AND IMPROVING THE DIELECTRIC CHARACTERISTICS OF SAID WINDINGS; SAID ADHESIVE COATING ON THE CONDUCTOR TURNS OF SAID FIRST AND SECOND WINDINGS PROVIDING THE ENTIRE BONDING ACTION BETWEEN SAID FIRST AND SECOND WINDINGS AND SAID FIRST AND SECOND TUBULAR INSULATING MEMBERS. 